Some gas analyzers using light absorption as disclosed in Patent Literature 1 use what is called a multipass cell which has a pair of mirrors arranged oppositely to each other in a cell main body, into which sample gas is introduced, to cause multireflection of light between the mirrors.
The use of the multipass cell as described above increases a light path length, thus permitting an increase in a distance of interaction between the light and the sample gas and permitting an improvement in sensitivity.
However, the multipass cell disclosed in Patent Literature 1 is of a type called a Herriot cell, which uses, as the pair of mirrors, spherical mirrors with reflecting surfaces of a circular shape in a plan view, so that a height and a width of the cell main body needs to be larger than those of the spherical mirrors, and there is limitation on a reduction in a volume of an inner space of the cell main body.
Consequently, there is also limitation on an improvement in a replacement speed of the sample gas introduced into the inner space, raising a problem of failure in obtaining a response speed required for analysis, for example, upon measurement of exhaust gas or the like whose discharge amount of each component fluctuates in accordance with a behavior of an internal combustion engine.